1. Field of the Invention
The present invention relates to an organic electroluminescent display device (OELD), and more particularly, to an OELD that has a recess or a groove in the surface of an insulating layer that is located at edges of a pixel electrode.
2. Description of the Related Art
An active matrix organic electroluminescent display device (AMOELD) includes a plurality of pixels arranged on a substrate. Each of the pixels includes at least one switching thin film transistor, a driving thin film transistor, a capacitor, and an organic electroluminescent element. The organic electroluminescent element includes a lower electrode which is a pixel electrode, an upper electrode which is a cathode electrode, and an organic layer including a luminescent layer interposed between the upper and lower electrodes whose edges are covered by a pixel definition layer.
If the organic electroluminescent element is applied a predetermined bias to an anode electrode having a high work function and the cathode electrode having a relatively low work function from the outside, a hole and electron are injected into the luminescent layer from the anode electrode and the cathode electrode, respectively, and light having a predetermined color is emitted by the combination of the hole and the electron that have been injected into the luminescent layer.
The luminous efficiency of the light emitted from the luminescent layer greatly depends on interfacial characteristics between the anode electrode and the organic layer, and influences the life span of the organic electroluminescent element. A variety of methods have been used to improve the luminous efficiency of the organic electroluminescent element.
Korean Patent Publication No. 2001-0057125 has proposed a method of fabricating an organic luminescent element to improve interfacial characteristics between the anode electrode and an organic layer by processing an indium tin oxide (ITO) film which is an anode electrode with SF6 plasma. Further, Japanese Patent Publication No. 2000-133466 has proposed a charge injection type luminescent element to improve interfacial characteristics between the anode electrode and an organic layer by applying oxygen ions or electrons onto an ITO film. What is needed is an improved structure for an OELD that results in improved interfacial characteristics between the anode and the organic layer.